DSCS-3

The DSCS III is the third generation of general purpose military communication
satellites. The first DSCS III was launched in 1982. In contrast to its predecessors, DSCS III offers significantly greater capacity and longer life, and
improved resistance to hostile activities such as jamming. The DSCS III
satellite, which has a design life of ten years, is designed to support all three
military services, and its signals can be received by ground antennas that range
in diameter from 33 inches to 60 feet. Signals are broadcast on 6 channels
between 7250 and 8400 MHz (television broadcasts between 54 MHz and 800
MHz). The satellite also carries a Single Channel Transponder (SCT) that is
used to transmit Emergency Action Messages from the President to nuclear
forces.

The DSCS III system is built with single- and multiple-beam antennas that
provide more flexible coverage than its predecessors. Phase III satellites bring
more capacity while providing greater assured communications through improved
ability to resist jamming. Antenna design for DSCS III allows users to switch
between fixed, Earth coverage, and multiple-beam antennas. The latter provides
an Earth coverage beam as well as electrically steerable area and
narrow-coverage beams. In addition, a steerable transmit dish antenna provides
a spot beam with increased radiated power for users with small receivers. In
this way, operators can tailor the communications beams to suit the needs of
different size user terminals almost anywhere in the world.(1)

The Air Force began launching the more advanced Phase IIIs in 1982. Previous
launch vehicles included Titan 34D/IUS and the Space Shuttle. The 3 October
1985 launch of the Space Shuttle "Atlantis" carried two Defense Satellite
Communications System (DSCS-III) satellites, which were propelled to geosynchronous orbit, 22,500 miles above the Earth by an Inertial Upper Stage
(IUS). Although NASA and the Defense Department continued their policy of not
announcing the payloads of military flights of the Shuttle, the payload of the
Atlantis was readily identifiable from public sources. An August 1981 Air Force
Space Division fact sheet on the DSCS program stated that the "first launch of a
DSCS III on the Shuttle is scheduled for mid-1985." A 1983 press report noted
that a "crucial launch appears to be scheduled in 1985, when a pair of DSCS
III's are to be launched from the Shuttle using and IUS booster."(2) And another
trade press report the following year noted that two DSCS III's would "be
launched together next year on a single Space Shuttle mission, apparently on
the Atlantis mission from the Cape in September."(3) Phase III satellites, with the
Integrated Apogee Boost Subsystem (IABS), are currently configured to launch
only on the Atlas II launch vehicle. The first Atlas II launch of a DSCS III
IABS occurred on 10 February 1992. Additional launches of these satellites are
planned at yearly intervals.

DSCS-3 spacecraft weigh 2,580 pounds, and have a design life of ten years,
twice as long as the Phase IIs. The spacecraft's rectangular body is 6 feet x 6
feet x 7 feet; with a 38-foot span with solar arrays deployed. Phase III solar
arrays generate 1,100 watts, decreasing to 837 watts after five years. Each
DSCS III satellite costs about $100,000,000.

DSCS III satellites (Phase III), which are now used
exclusively, were first placed in operation in 1983; nine are currently active (five primary and four
reserve), and five are in inventory. The most recent launch was in October 1997 (B-13). Future DSCS III launches are tentatively scheduled for
1999 (B-8), 2000 (B-11), 2002 (B-6), and 2003 (A-3). DSCS III satellites, designed to provide
SHF SATCOM capability through the year 2000 and beyond, are being placed in geosynchronous
orbital positions 22,300 miles above the equator to provide coverage between 75 o north latitude and
75 o south latitude. The DSCS constellation provides communications services in each of the following
five satellite areas: East Pacific (EPAC), West Atlantic (WLANT), East Atlantic (ELANT), Indian
Ocean (IO), and West Pacific (WPAC).

DSCS III Footprint

There are two series of DSCS III satellites: A-series and B-series. The A-series
are the first-generation DSCS III satellites. The B-series are newer and have received upgrades
to various support subsystems and the communications subsystem (Note: Model A-3 awaiting launch
will be upgraded and have the same capabilities as a B-series model). The essential difference between
the A-series and B-series DCSC III satellites is in the single channel transponder (SCT) package. The
A-series DSCS/ SCT has only the UHF downlink capability while the B-series DSCS/ SCT has both
UHF and SHF downlink capability. Thus, when the Navy is operating over DSCS III B-series channel
one, the regular communications channel will have to share the channel one traveling wave tube
(TWT) power amplifier with the SCT community; however there is no power sharing required with the
SCT community over the DSCS III A-series satellites. The DSCS III satellites are designed for an operational life span of 10 years.

Current DSCS Satellite Constellation

SATELLITE OCEAN AREA

DSCS III SATELLITE
MODEL

LONGITUDE (Degrees)

East Pacific Primary

B-14

135W

East Pacific Reserve

A-1

130W

West Atlantic Primary

B-7

52.5W

West Atlantic Reserve

B-4

42.5W

East Atlantic Primary

B-12

12W

Indian Ocean Primary

B-10

60E

Indian Ocean Reserve

A-2

57E

West Pacific Primary

B-9

175E

West Pacific Reserve

B-5

180E

DSCS III Satellite Capability. The DSCS III satellites provide substantial capability to
support high-capacity links between all terminals and to permit AJ communications and control of the
satellites during crisis and contingency situations. DSCS III satellites operate in the X-band region,
providing uplink services in the 7900-8400 MHz band and downlink services in the 7250-7750 MHz
band. The frequency spectrum is divided into six bands by the use of six limited-bandwidth
transponders which are switchable between antennas by DSCS ground control. Communications
performance is optimized by allowing these independent transponders to be connected to various types
of antennas. This permits selection of Earth coverage (EC), area coverage (AC), spot coverage,
grouping of channels with similar modulation, and antenna gain-to-noise temperature (G/ T) ratios to
meet user needs. Any type of modulation or multiple access may be used since the transponders do not
process or modulate the signals. The DSCS III satellites are three-axis stabilized (geostationary)
vehicles that have a dry weight of 1,950 pounds and a maximum weight of 2,550 pounds with
propellant. The dimensions of the satellite body are approximately 80 inches (6.5 feet) on each side
and 460 inches (38 feet) in length, with solar arrays (SA) deployed. Communications antennas include
a receive 61-beam multibeam antenna (MBA) and two transmit 19-beam MBAs, two receive and two
transmit Earth coverage horns (ECH), and a transmit-only gimballed dish antenna (GDA). In addition,
there is one transmit and one receive SCT UHF antenna.

Attitude Control Subsystem (ACS). The ACS is a three-axis, zero momentum
stabilization system using on-board electronic processing to provide attitude control. The ACS orients
and stabilizes the satellite after launch vehicle separation, maintains pointing during on-orbit and
payload operations, and controls the satellite attitude during orbit adjustment operations.

Propulsion Subsystem (PS). The PS consists of four propellant tanks, two thruster
banks (eight thrusters each bank), and six propellant fill and drain valves. Individual thruster banks are
capable of performing all mission functions.

Telemetry, Tracking and Command (TT& C) Subsystem. The TT& C subsystem
provides the capability to command the satellite and transmit TT& C data over redundant control links.
The TT& C is a secure (encrypted) telemetry link used primarily for command and control of
communications payload operations and on-orbit testing. (Chapter 3 of this NTP provides additional
information on DSCS control.)

Electrical Power and Distribution Subsystem (EPDS). The EPDS provides for the
conversion of solar energy to electrical power and the regulation and distribution of power to the other
satellite subsystems. EPDS also provides storage of electrical energy for subsequent use by other
subsystems throughout satellite mission life.

Structures and Mechanisms Subsystem. The major fixed structural assemblies of the
DSCS III satellites include a central bay structure, north and south panels, antenna supports, solar array
substrates, and a launch vehicle adapter. The main body structure provides hard point mounts for the
propulsion system and the communication antennas. The center bay is constructed of aluminum
honeycomb panels for mounting components.

DSCS III Communications Subsystem

The DSCS III Communications Subsystem includes six
independent RF channels, jammer location electronics (JLE), one receive 61-beam MBA, two receive
ECHs (E1R and E2R), two transmit 19-beam EC/ narrow coverage (NC) MBAs (M1X and M2X),
one transmit GDA, and two transmit ECHs (E1X and E2X). Channels 1 and 2 are designated as high
power channels and each operates with a 40-watt TWTA. Channels 3 to 6, the low power channels,
operate with a combination of 10-watt TWTAs/ high efficiency solid-state amplifiers (HESSA), and
linear solid-state amplifiers (LSSA). The last four DSCS III satellites
scheduled for launch (B-8, B-11, B-6, and A-3) will receive performance upgrades through the DSCS
SLEP. Responding to the Services' need for more capacity, the original DSCS III SLEP has been
revised. The revised SLEP provides improved satellite capability for the next four DSCS satellites to
be launched with the first scheduled in July 1999 and the fourth in fiscal year (FY) 2003 (a fifth satellite
is currently unfunded). Major revised SLEP upgrades to the DSCS III satellite include increased
transponder bandwidth and 50-watt TWTA in all six channels. The 50-watt TWTA and bandwidth
addition is predicted to provide a 700 percent increase in tactical communications capacity.

Furthermore, upgrades to the low noise amplifiers (LNA) is estimated to provide an approximately 30
percent increase in data rates for smaller terminals. The increased power capability in all channels on
SLEP DSCS III satellites will allow shifting of nontactical users on channels 2 through 4 to channels 5
and 6 by using bandwidth-efficient modulation techniques. This compression technique provides
greater bandwidth utilization but, in the past, was not feasible due to the increased power-per-bit
requirement. SLEP will increase the mean mission duration (MMD) from 7.5 to 10 years per satellite. The downlink EIRP for SLEP-modified
DSCS III satellites is to be determined.

ITEM

KEY FEATURES

DSCS
Receive
Antennas

One 61-beam waveguide lens, MBA
Full 61-beam control of amplitude and phase
Broadband, selective nulling
Accurate, rapid control of selective coverage pattern
Two EC horn antennas

DSCS III Communications Channel Block Diagram

DSCS III Satellite Block Diagram

The six independent RF channels operate in the SHF band to relay telephone, data, wideband
imagery, and secure digital signals. Figure 2-3 shows a typical DSCS III communications subsystem
functional block diagram for an individual channel composed of the receive antenna, transponder,
frequency standard, frequency generator, and transmit antenna. Figure 2-4 shows the functional
relationship of each of the major components that make up the communications subsystem. The
communications subsystem operates in the X-band region. The uplink and downlink frequency plan
used in the DSCS III satellite Models A-1, A-2, B-4, B-5, and B-7 is illustrated in figure 2-5. Four of
the six RF channels have 60-MHz bandwidth. Channel 3 has an 85-MHz
bandwidth, and channel 6 has a 50-MHz bandwidth. The total usable bandwidth is 375 MHz. These
six RF channels are arranged with uniform 25-MHz guard bands between them. Each uplink channel
frequency is translated down by 725 MHz on the downlink with the exception of channel 6, which is
translated by 200 MHz. The newer DSCS III satellites including B-9, B-10, B-12, and B-14 (and
Models A-3, B-6, B-8, B-11 and B-13 awaiting launch) provide an improved satellite channelization
with a total usable bandwidth of 405 MHz, as depicted in figure 2-6. Under this new frequency plan,
the bandwidth of channels 2 and 4 is increased through a reduction in the size of the guard bands and a
decrease in the bandwidth of channel 1. Channel 1 has a 50-MHz bandwidth; channel 2 has a 75-MHz
bandwidth; and channel 4 has an 85-MHz bandwidth. There is a 15-MHz guard band between
channels 1, 2, 3, and 4; and a 25-MHz guard band between channels 4, 5, and 6.

DSCS III Frequency Plans

The communications subsystem partially supports the TT& C subsystem, as well as the SCT
subsystem. Communications operations can be conducted simultaneously with TT& C and SCT
operations without mutual interference. TT& C commands are received by the satellite through the
communications subsystem's receive MBA or receive EC antenna. Two telemetry uplinks are received
at separate frequencies, one in the communications subsystem channel 1 and the other in channel 5.
Each input signal is fed through the communications transponder front-end which provides
preamplification and filtering. The output signal is then downconverted in two steps to the
intermediate frequency (IF) input required by the TT& C COMSEC equipment (redundant KI-24s for
decrypting and encrypting). The plain text output of the KI-24 is fed to the command and telemetry
unit (CTU) for decoding and distribution to the intended subsystem for execution. The telemetry link
is used primarily for normal command and control of the satellite support subsystems and also during
vehicle anomalies. It supports Space Ground Link Subsystem compatible pseudorandom noise
turnaround ranging, coherent Doppler tracking, noncoherent telemetry, secure encrypted or plain text
telemetry transmission and command reception. The telemetry link uses crossed-dipole antennas
mounted on opposite sides of the satellite to provide near spherical coverage. Redundant receivers
provide carrier lock, and demodulate ranging and command signals. Command data cipher text is fed
to the CTU which routes it to a preselected KIR-23 decoder for distribution to the intended subsystem
for execution.

DSCS III satellites currently in use are equipped with two high power 40-watt TWTAs, channels
1 and 2, and four low power 10-watt TWTAs/ HESSAs for channels 3-6. A steady growth in user
requirements has necessitated additional design improvements, including the modification and
replacement of the 10-watt HESSAs with 16-watt LSSAs for use in channels 5-6. The last four DSCS
III satellites scheduled for launch (B-8, B-11, B-6, and A-3) will receive SLEP modifications which
include the replacement of all high power amplifiers (HPA) with 50-watt TWTAs, providing
significantly greater linear output power than is available from either the 10-watt HESSAs or 16-watt
LSSAs.

DSCS III HPA Configurations

Two low power channels (channels 5 and 6) are dedicated to EC reception and transmission
using EC horns. These horns are designated E1R and E2R for reception and E1X and E2X for
transmission. Channels 1 and 2 (high power) and 3 and 4 (low power) can be commanded from the
ground to connect to the EC horn receive antennas or to the 61-beam receive MBA. For
transmission, channels 1 and 2 are connected to the two 19-beam MBAs (E1X and E2X) or to the
GDA. Channels 3 and 4 have the option of connecting to EC horns or sharing a 19-beam transmit
MBA with a high power channel. In addition, channel 4 may also be switched to the GDA.

The communications subsystem may simultaneously employ full Earth coverage, area coverage,
and narrow coverage modes for transmission and reception. Using the MBAs, the capability exists to
provide narrow coverage, area coverage, or selectively shaped area coverage by combining multiple,
simultaneous narrow coverage patterns. A high gain, narrow transmit coverage capability is provided
by the GDA.

The receive MBA capability includes the ability to eliminate or reduce the effect of jammers by
putting them in a null between sidelobes of an NC beam or by forming nulls in a broad area (up to full
Earth coverage) antenna pattern. The receive and transmit MBAs have the ability to simultaneously
cover multiple areas, thereby maximizing link gain between terminals in the illuminated areas and
reducing the effect of off beam jamming signals. This capability is not normally used during naval
operations, but may be employed as directed for contingencies.

Each transponder channel is capable of relaying, with minimal performance degradation, time-division
multiplexer (TDM)/ FDMA, CDMA, and time-division multiple access (TDMA) signals.
When relaying FDMA signals, the transponder HPA must operate in an essentially linear mode.
CDMA and TDMA signals permit operation in a near-saturated mode. The gain of the transponder is
controlled prior to the TWTA/ HESSA to ensure the desired degree of TWT saturation for varying
input levels. Input variations depend on the number of uplink signals and the EIRP of the Earth
terminals.